Exercise training has been reported to be beneficial in preventing and/or treating cardiovascular disease. However, the underlying mechanisms and relative importance of training induced changes in the cardiovascular system are not clear at this time. The primary objectives of this proposal are to determine: 1) the mechanisms involved in providing adequate nutrient and metabolite transport in skeletal muscle and coronary vascular beds during normal exercise and 2) the influence(s) of chronic exercise training on these phenomenon. The specific aims that the research outlined in this proposal will accomplish can be divided into two major areas. Skeletal muscle vascular bed. These studies will determine the mechanisms responsible for directing blood flow to active oxidative muscle fibers within muscles during running and determine the effects of exercise training on the vascular transport capacity of skeletal muscle tissue. The hypotheses to be tested are: a) the sympathetic nervous system controls blood flow within muscles during exercise. b) the release of vasoactive metabolites from the active oxidative muscle fibers controls blood flow distribution during exercise. c) Blood flow is controlled within muscles during exercise by neurohumoral mechanisms. d) Exercise training causes an increased transport capacity in the deep red muscles. e) Functional capillary surface area is increased in the red muscles of exercise trained rats. Coronary Circulation. The coronary studies are designed to determine the mechanisms responsible for the exercise training induced increase in coronary transport capacity and its physiologic significance. The hypotheses to be tested are: a) Coronary transport capacity is increased due to increased coronary capillary surface area and altered sympathetic neural control of the coronary vascular bed. b) The training induced increase in coronary transport capacity observed in dogs will be observed in other mammals. c) The increased coronary transport capacity will be protective during acute myocardial ischemia due to controlled partial coronary occlusion. The results of these experiments will further our understanding of the influences of exercise and exercise training on cardiovascular function.